Still in the Render Setup window, proceed to the Indirect Illumination tab and make sure Enable Final Gather, Caustics and Global Illumination are all turned off (Fig.36).

Fig. 35

Then proceed to the Render Elements tab. You'll need three additional render passes for this tutorial: A Matte to separate the city from the sky so we can do an effective sky replacement, an Occlusion Pass to fake global illumination and a Z-Depth Pass to be able to add an atmospheric effect and some depth of field.

Step 4.1: Occlusion Pass

Name the pass Occlusion and under Parameters press the button next to Shader to add a new shader. Choose Ambient/Reflective Occlusion from the list. There are a lot of settings to play with to tweak the Ambient/Reflective Occlusion shader, but the standard settings, although a little rough, will do just fine for this tutorial (Fig.38).

Fig. 37

This basically renders a pass of the scene where this texture is applied to all geometry (Fig.39).